Install green bridges as road/railway crossing structures for bats

Overall effectiveness category Unknown effectiveness (limited evidence)
Number of studies: 1
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How is the evidence assessed?

Effectiveness

70%
Certainty

27%
Harms

0%

Calculating overall effectiveness category

Background information and definitions

Green bridges are bridges over roads/railways that are covered in vegetation and usually planted with hedgerows and trees. They have been built as mitigation measures usually to guide larger mammals, such as deer, safely across wide roads or railways. A study in Germany found 10 bat species using eight green bridges to fly over a road and also to forage (Bach & Müller-Stiess 2005). However, the study has not been summarised here as it did not provide data that can be used to assess effectiveness, such as a control, or the proportion of bats not using the green bridges. The study described below reports the proportion of bats that are either using a green bridge to cross the road safely or are crossing the road below at risk of collisions with traffic.

Bach L. & Müller-Stiess H. (2005) Technical article bats on selected green bridges. Efficiency of wildlife passages in Baden-Württemberg. Fachbeitrag Fledermäuse an ausgewählten Grünbrücken. Effizienzkontrolle von Wildtierpassagen in Baden-Württemberg (FE 02.220/2002/LR) In: Georgii B., Peters-Ostenberg E., Henneberg M., Herman M., Müller-Stiess H. & Bach L. (2007) Nutzung von Grünbrücken und anderen Querungsbauwerken durch Säugetiere. Gesamtbericht zum Forschungs- und Entwicklungsvorhaben 02.247/2002LR.

Study locations

Key messages

One study evaluated the effects of installing green bridges as road crossing structures for bats. The study was in the UK.

COMMUNITY RESPONSE (0 STUDIES)

POPULATION RESPONSE (0 STUDIES)

BEHAVIOUR (1 STUDY)

Use (1 study): One study in the UK found that a green bridge was used by 97% of bats crossing a road.

About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

A study in 2014 at one green bridge over a road in the UK (Berthinussen & Altringham 2015) found that the green bridge was used by 97% of bats that crossed the road. A greater number of bats crossed the road using the green bridge (97%, 121 of 125 bats) than crossed the road below at traffic height (2.4%, 3 of 125 bats) or above traffic height (0.8%, 1 of 125 bats). Four bat species were recorded using the green bridge for crossing and foraging: common pipistrelle Pipistrellus pipistrellus (92 bats), soprano pipistrelle Pipistrellus pygmaeus (22 bats), Natterer’s bats Myotis nattereri (2 bats), and a whiskered or Brandt’s bat Myotis mystacinus or Myotis brandtii (1 bat). Four bats using the green bridge could not be identified to species. One common pipistrelle and two unidentified bats were recorded crossing the road below the green bridge at traffic height. One common pipistrelle crossed the road below above traffic height. The green bridge was built over a four-lane road in 2005 to maintain access to a historic property and provide a wildlife crossing. The bridge (50 m long x 30 m wide x 6–8 m high) had a paved road over it with grass verges, shrubs, and trees (2–3 m high) on each side. Observations of crossing bats and recordings of bat calls were made during 10 x 60-minute surveys at dusk or dawn in June–August 2014.
Study and other actions tested
Referenced paper
Berthinussen A. & Altringham J. (2015) Development of a cost-effective method for monitoring the effectiveness of mitigation for bats crossing linear transport infrastructure. DEFRA report, WC1060.

Please cite as:

Berthinussen, A., Richardson O.C. and Altringham J.D. (2021) Bat Conservation: Global Evidence for the Effects of Interventions. Conservation Evidence Series Synopses. University of Cambridge, Cambridge, UK.

Where has this evidence come from?

List of journals searched by synopsis

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This Action forms part of the Action Synopsis:

Bat Conservation

Related Actions

Actions	Effectiveness	Studies	Category
Maintain bat roosts in road/railway bridges and culverts Action Link	Likely to be beneficial	2	Synopsis Link
Change timing of maintenance work at road/railway bridges and culverts Action Link	No evidence found (no assessment)	0	Synopsis Link
Install underpasses or culverts as road/railway crossing structures for bats Action Link	Likely to be beneficial	8	Synopsis Link